Method of making absorbent bearing products

ABSTRACT

Particulate absorbents of a water-insoluble water-swellable polymer having a gel capacity of at least 10 are immobilized with a composition comprising the absorbent in a liquid polyhydroxy organic compound. The composition may be employed by applying to an appropriate surface and subjecting the liquid film to solidifying conditions. The solidified film product has high absorptive capacity and is free of undesirable movement when positioned in absorbent articles. A foam product having both absorptive and cushioning properties is prepared from a solid, particulate, water-insoluble, water-swellable polymer having a gel capacity of at least 10, a solid, particulate blowing agent, and a liquid polyhydroxy organic compound.

This is a continuation-in-part of application Ser. No. 274,232, June 22,1981 which in turn is a continuation-in-part of application Ser. No.181,289, filed Aug. 25, 1980 and Ser. No. 248,387, filed Mar. 27, 1981and now abandoned.

The present invention relates to absorbent products, compositions andmethods for immobilizing particulate absorbents and absorbent articlesproduced therefrom and to methods for producing certain absorbentproducts.

Absorption of mobile aqueous liquids have conventionally beenaccomplished by the use of sponge or batting. More recently,water-insoluble but water-swellable polymers having high absorptivecapacity have been developed for immobilizing water and aqueous fluids.These polymers are particulate, i.e., pulverulent or granular and haveno structural integrity. They are frequently referred to in the art as"superabsorbents," "hydrogels" or "hydrocolloids" and have beenincorporated in the cellulosic absorbent structure in diapers, sanitarynapkins and other absorbent articles to increase their absorptiveefficiency. The expected advantage of incorporating these particulatematerials is diminished by the shifting of the particulate materialsgenerally requiring special construction to immobilize them within thestructure of the articles. A process for decreasing the mobility ofparticulate absorbent materials and products in which the particulateabsorbents are uniformly retained is desirable. In U.S. Pat. No.3,900,030, there is described a catamenial tampon which utilizes anopen-celled polymer foam which has the water-swellable polymers imbeddedtherein. While this provides structural integrity to the absorbentpolymer, versatility in application is governed by the foam carrier.Moreover, the method of disposition is dictated by the foam carrier.

DESCRIPTION OF THE INVENTION

In accordance with the present invention it has been discovered that bymixing together a particulate, water-insoluble water-swellable polymerabsorbent and a liquid polyhydroxy organic compound the polymerabsorbent may be immobilized. Immobilizing compositions comprising thepolymer absorbent and liquid polyhydroxy organic compound may beemployed to form novel products in which the absorbent has beenconverted to a non-particulate immobilized form, i.e., an absorbentbearing solidified structure. When the composition includes a blowingagent, the composition is a foamable immobilizing composition and theabsorbent bearing solidified structure is a foam product. In theabsorbent-immobilizing compositions, at least 25 to no greater than 125,preferably from about 40 to 80 parts by weight of the polymer absorbentare employed for every 100 parts by weight of the liquid polyhydroxyorganic compound. The composition suitable for the preparation of foamproducts contains in addition from about 2 to about 30 parts by weightof blowing agent. The absorbent-immobilizing composition with or withoutblowing agent (a) may be cast, coated or cold extruded on an appropriatesurface to obtain free films or sheets, (b) may be coated on theultimate surface, e.g., substrate to form a film coating or (c) if afoam-forming composition, also may be foamed in place. The products havestructural integrity on solidification, have superior absorptiveefficiency, are self-supporting, and are degradably disposable ashereinafter described.

The absorbent products are structurally stable solids, resilient andsomewhat elastic, which rapidly swell on absorption of fluid. They havethe property of being degradable in large excess of water towater-dispersible particles, providing a convenient means fordisposition after the desired function has been accomplished. When theabsorbent product is a foam product, it differs from conventional spongeor solid foam in having an extremely high capacity for absorbing aqueousfluids, being limited by the absorptive capability of the polymerabsorbent and not by the dimensions of the original foam structure. Theproducts are also advantageous in being easily prepared from a non-toxicliquid foam-forming composition which is readily manageable without thenecessity of adding water or organic solvent. Absorbent articles havingparticulate absorbents immobilized by an absorbent-bearing solidifiedstructure according to the present invention have high absorptivecapacities which are not diminished by shifting and bunching ofparticulate absorbents accompanying transportation and handling prior touse. Moreover, the rate of absorption is substantially undiminished bythe presence of a solidified structure enveloping the absorbentparticles. The uptake of aqueous liquid is substantially instantaneous.This is wholly unexpected inasmuch as the presence of a carrier usuallydecreases the absorption rate.

The absorbent products are useful as the sole or supplementary absorbentpanel material in absorbent articles such as bed pads, sanitaryproducts, diapers, incontinence pads and the like. When the absorbentproduct is to be used as the sole absorbent panel, it may be applieddirectly to the ultimate substrate to be employed in the absorbentarticle, e.g., a diaper backing. Substrates suitable for such purposesinclude, for example, film such as polyethylene film, non-wovencellulosic materials, wood-pulp materials and the like. However, it maybe employed in combination with wood-pulp panels used in batting andwith other absorbent materials while still having the effect of reducingsize or thickness. The product when foam, not only has superiorabsorptive capabilities but has a soft feel and resilience therebyproviding comfort without the thickness of conventional batting. Arelated application employing the absorbent product, especially in theform of foam, on a flexible substrate is in medical or surgicaldressings and sponges.

When the product is a foam, its resilient and somewhat elastic naturerenders it also useful in applications where both absorption andcushioning is desired such as in packaging, particularly for odd shapestructures. Since the foam may be prepared from nontoxic materials, itis readily adaptable to foaming-in-place. However, the foam is stableand may be prepared in any size and shape, and stored with or withoutsupporting structure. If desired it may be cut to the desired form forultimate use.

An application of combined absorption and cushioning use is as aprotective liner in dual-walled or dual containers for transportingaqueous fluids in which the inner wall or inner container is ofbreakable material such as glass used in transporting radioactivesolutions or biological fluids. If the containers require specialmaterials such as outer lead containers for radioactive fluids, it isdesirable to reuse the load container; the foam product is advantageousin being readily removable from the container by flushing the containerwith excess water.

The expression "absorbent" refers to water-insoluble, water-swellablepolymers as hereinafter described having an enhanced capacity forremoving water or aqueous fluids. The water-insoluble, water-swellablepolymers are lightly cross-linked polymers containing a plurality ofhydrophilic groups, such as carboxyl, carboxamide, sulfonate salt orhydroxyl groups, along the polymer chain in sufficient proportions sothat the polymer would be water-soluble if it were not for thecross-linking thereof. In these polymers, the hydrophilic groupsconstitute at least twenty-five percent and up to seventy-two percent oftheir molecular structure. The materials are of sufficient molecularweight or degree of cross-linking to be water-insoluble while beingwater-swellable. Many of the suitable materials are those which havebeen reported to have an average molecular weight per cross-linkage inthe range of from about 13,000 to about 300,000, but are not limitedthereto. The most common and best known of such materials arepolyacrylate modified polysaccharides, cross-linked syntheticpolyacrylates, cross-linked carboxymethylcelluloses or cross-linkedpoly(alkylene oxide)s as hereinafter defined. Other graft polymers ofpolysaccharides and natural gums such as xanthan gum, locust gum, guargum and the like or blends thereof are also suitable provided they meetthe requirements of water insolubility and water swellability. Thewater-insoluble, water-swellable polymers have a gel capacity of atleast about 10. By "gel capacity" is meant the weight of aqueous fluidwhich can be imbibed and held per unit weight of polymer, i.e., grams offluid per gram of polymer. Stated another way, the absorbent polymershave an absorbent capacity of at least 10 times the weight of thematerial in dry form. The capacity may be up to 1500 times or more ofthe weight of the material in dry form; commonly it is about 15 to 70times the dry weight. The materials are frequently spoken of in the artas "hydrogels", hydrocolloids" or "superabsorbents". Many of thewater-swellable polymers are available commercially.

The polymers are used in particulate form. By "particulate" is meant asubstance in the form of fine discrete particles. They may be variouslyshaped such as spherical, rounded, angular, acicular, irregular, orfibrous. The particles generally range in size from about 1 micron to2×10⁴ microns in diameter or cross-section (largest dimension when notspherical). The particles are preferably of finely divided powder ofparticles size of from about 1 to about 10³ microns.

By "absorbent-immobilizing composition" is meant a compositioncontaining a water-insoluble water-swellable polymer in particulate formand a liquid polyhydroxy organic compound and which may contain ablowing agent and/or minor amounts of non-essential additiveshereinafter detailed. The composition is the vehicle for immobilizingparticulate absorbent.

The liquid polyhydroxy organic compound employed in the presentinvention is a high boiling liquid having at least two hydroxy groups,preferably vicinal or adjacent hydroxy groups. Suitable liquids includeglycerol, ethylene glycol, propylene glycol, and the like. Glycerol andethylene glycol are preferred.

The blowing agent in the foamable absorbent-immobilizing compositionsmay be any non-gaseous agent decomposing to form a gas and includessodium bicarbonate, azo compounds, such as azodicarbonamide,p-toluenesulfonyl semicarbazide, p,p-oxybisbenzenesulfonyl hydrazide,p-toluenesulfonyl hydrazide and the like. In certain aspects of thepresent invention, a non-foamable absorbent-immobilizing composition maybe employed and the blowing agent may be a gas such as air, nitrogen,carbon dioxide and the like.

In addition to the foregoing components, the composition may haveincluded therein minor amounts of other additives which may impartdesirable properties to the absorbent product. Thus, a surface activewetting agent, particularly non-ionic surface active agent may beincluded to enhance liquid uptake. A surface active agent is ofparticular advantage in assisting vertical transport of liquids.Representative surface active agents are those commonly described suchas alkyl aryl polyether alcohols or alkylphenyl ethers of polyethyleneglycol, e.g., reaction product of t-octylphenol or nonylphenol withethylene oxide. Fine fibrous cellulose such as cellulose flour,silicates and the like also have similar effect. Activated charcoal orother adsorbent may be included for odor uptake. Fragrance, coloring,etc., may be included for a pleasing effect. Inert materials containingbound water such as silicates, aluminum hydrate and the like may beemployed to modify the texture of the sheet. Similar results may beachieved employing slightly wet ethylene glycol or glycerol, e.g.,commercial glycerine. If the absorbent immobilizing composition containsa low level of pulverulent absorbent, there is a slight tendency for theabsorbent to settle. The composition may be modified to include smallquantities of materials to affect its spreading properties. Suitableviscosity modifiers include silicated powders, clays, zinc oxide, inertfillers and like materials. Also, the polyhydroxy compounds may bemodified with minor amounts of liquid modifiers such as ether glycols,mineral oil, etc., not contemplated as the essential component of theinstant compositions. Generally, the additives, if employed, do notconstitute more than about 25 percent of the total composition.

By "absorbent-bearing solidified structure" is meant the solid resultingon solidification of the liquid composition after application to asubstrate or carrier surface, or to a metal or release coated surfacefor free film, sheet or foamed sheet formation, or also if foamablecomposition after application to a container. When the absorbent bearingsolidified structure is a film or sheet, whether foam or non-foam, itmay be in the form of a continuous film or a discontinuous one; it mayhave a lattice-like form. Also, as hereinafter described, it may be inthe form of a filament. The term "film" as herein employed contemplatesa thickness up to about 10 mils. The term "sheet" contemplates athickness greater than 10 mils and may be non-foam or foam. Preferredstructures are sheets, both foam and non-foam.

The process of immobilizing particulate absorbent and forming anabsorbent bearing solidified structure is carried out by applying anabsorbent-immobilizing composition comprising an absorbent and a liquidpolyhydroxy organic compound, prepared by mixing the components togetheronto a temporary or ultimate surface. The amount of absorbent employeddepends in part on the viscosity of the liquid polyhydroxy organiccompound used as vehicle as well as on the amount desired in theultimate product while within the range previously set forth.

When the absorbent bearing solidified structure is a foam, it may beprepared by mixing the components in any sequence to obtain anabsorbent-immobilizing foamable composition and then subjecting thecomposition to foaming conditions to obtain the desired foam product.Thus, it may be prepared by first mixing together an appropriatewater-insoluble, water-swellable polymer and blowing agent, thereafteradding a liquid polyhydroxy organic compound to the dry mixture and thenstirring until homogeneous to obtain a foamable absorbent-immobilizingcomposition. Alternatively, the polymer and the liquid polyhydroxyorganic compound may be mixed together and the blowing agent thereafteradded to obtain a foamable absorbent immobilizing composition. A foamstructure also may be prepared from a non-foamable composition assubsequently detailed.

Compositions of polymer absorbent in liquid polyhydroxy organic compoundhave time-limited fluidity and mobility. They are preferably preparedwithin several hours prior to use or at least within 24 hours but someabsorbent-immobilizing compositions remain in the liquid form for longerperiods.

The liquid absorbent-immobilizing composition then may be applied to atemporary or ultimate surface. The ultimate surface is hereinafterreferred to as substrate. For making a film, sheet, foam sheet or coatedsubstrate, any method of application conventionally employed for coatingor preparing films, e.g., knife-coating, spray-coating, reverse-rollcoating, gravure-coating, cold extrusion coating or casting, and thelike, may be employed. Preferred methods are cold extrusion coating andknife-coating. The cold extrusion coating method may be employed toprepare a foam structure from the immobilizing composition which doesnot contain a particulate blowing agent. In this procedure, inert gas asblowing agent is injected downstream into the extruder chamber at apoint where mixing has been completed to foam the mixture and to producea viscous foamed extrudate which then may be coated in any manner.Another method of making a foam structure from an immobilizingcomposition which does not contain a blowing agent is to whip air intosaid composition and thereafter coating in any manner.

For making absorbent foam sheets or strips, a continuous processemploying a cold extruder with a heated die is especially convenient. Inthis process, the components, namely, a particulate water-insoluble,water-swellable absorbent polymer, a liquid polyhydroxy organic compoundand a blowing agent as essential components, together with a minoramount of wetting agent and other optional additives are fed into anextruder, and then passed through the extruder barrel at ambienttemperature to intimately mix the components, the mixture thereafterforced into a die maintained in the temperature range of from about 200°to 400° F. whereupon blowing occurs with the formation of solid foamproduct, and the foam product then expelled through the die orifice ontoa permanent or temporary substrate. The place for dispensing the blowingagent is dependent on whether a gaseous or non-gaseous blowing agent isemployed. If a solid or liquid, it is fed into the hopper of theextruder. If a gas, it is injected at a point downstream in the extruderchamber. The die may be a single slot die if foam sheets are desired anda multi-slot die if strips are desired. The substrate may be theultimate or permanent substrate in which case the foam layer is a foamcoating on the substrate, or the substrate may be a temporary substratesuch as a silicone liner if an unsupported foam sheet is desired.

When use as a coating on a substrate is contemplated, the substrate isof materials generally employed for absorbent articles, such ascellulose, vinyl films, polypropylene, polyester, polyethylene, nylon,metal foils, elastomers, cloth, nonwovens of various fibers, and thelike. Coating on a substrate may be of the entire surface of thesubstrate, in strips or in any other pre-determined pattern. When use asa free film, sheet or foam sheet is contemplated, the coating may bemade on material previously coated with a release agent such as siliconeor on a metal surface. When the immobilized absorbent structure is foamto be used in an irregularly shaped device, the liquid composition maybe poured into the irregularly shaped area. The coated substrate, thecoated sheet-forming surface, or the foamable composition contained inan irregularly shaped device is then subjected to time-temperaturerelated conditions to transform the liquid composition into a solidimmobilized absorbent structure in the form of a film, sheet, coating orfoam product.

The conversion of the liquid absorbent-immobilizing composition from aliquid-solid mixture to a solid film, sheet or foam may take place at atemperature up to 175° F. in a period as short as 15 minutes but moreusually over a period from about 30 minutes to 24 hours, or at elevatedtemperatures, 175° F. to 450° F. (79° C. to 111° C.), preferably about275° F. to 400° F. (135° C. to 204° C.) for a period of from a fewseconds up to about 15 minutes. In producing foam, the foamableimmobilizing composition may be placed in an appropriate vessel or ontoa substrate or surface for foaming, and allowed to foam at theappropriate temperature. Where speed is desired, transformation of theliquid composition to a solid may be accomplished by exposure to heat inthe range of about 200° F. to 450° F. (93° C. to 111° C.) for about 1 to60 seconds.

A factor affecting rate of solidification in addition to temperature isthe amount of polymer absorbent. Compositions with high absorbentcontent, e.g., greater than about 50 parts per 100 parts of liquidpolyhydroxy compound, solidify at ambient temperature in time measuredin hours but with lower amounts of absorbent, there is increase in thetime necessary for completion of a solidified structure formation. Thesolidified structure has been found to be more quickly formed from themore viscous liquid polyhydroxy compounds. However, the ultimate polymerabsorbent content of the solidified structure is generally lower withthe more viscous polyhydroxy compound since it is difficult to form ahomogeneous composition. Thus, for example, a film or foam obtained fromglycerol as polyhydroxy compound generally has less absorbent than thatfrom ethylene glycol as polyhydroxy compound. However, as previouslyindicated, for maximum absorptive efficiency of the ultimate product, itis desirable that the liquid polyhydroxy compound be the majorcomponent. Preferred films or sheets, whether foamed or not, are thosecontaining from about 40 to 80 parts by weight of absorbent per 100parts by weight of polyhydroxy compound.

The particulate absorbent in the absorbent-bearing solidified structureis firmly retained in the film or lattice and is not subject to movingor shifting in the ultimate absorbent article and retains all the highabsorptive capacity of the particulate absorbent.

The liquid absorbent-immobilizing composition particularly withoutblowing agent, in addition to being useful as starting material for thesolidified absorbent bearing film or structure above described, is alsouseful in the liquid form and may be applied to dressings, skin, bodyexudates as well as to aqueous liquids from other sources.

Many water-insoluble, water-swellable polymers suitable as absorbent areavailable commercially. They also may be prepared by cross-linking apre-formed water-soluble, straight chain polymer, by polymerizing anappropriate monomer or a monomer with a co-monomer to effectsimultaneous polymerization and cross-linking, or by incorporating ahydrophilic group into a completed polymer. An example of a laterincorporation of a hydrophilic group to the completed polymer is theincorporation by sulfonation of a sulfonic acid moiety. When it isdesired to have the hydrophilic group in the salt form, the polymer maybe prepared first as an acid, ester, amide, or nitrile and the producthydrolyzed in whole or in part.

The preferred polymers have an acrylate group in their molecularstructure. They may be completely synthetic acrylate polymers oracrylate modified polysaccharides, e.g., acrylate modified starch oracrylate modified cellulose. By "acrylate modified" is meant that anacrylate polymer or polyacrylate as hereinafter described has beengrafted onto the polysaccharide. "Acrylate polymer" or "polyacrylate" asherein employed embraces not only polymers which contain acrylate saltgroups but those which also may contain an acrylamide, acrylic acid,acrylic ester group or acrylonitrile group.

The preferred synthetic acrylate polymer absorbents are those which havea salt group, an acid group, or which have both an amide group and asalt or acid group. These have been represented in the literature, e.g.,U.S. Pat. No. 3,686,024, by the following formula: ##STR1## where A isan alkali metal ion such as sodium or potassium, or is hydrogen, n isfrom about 0.5 to about 0.9, 1-n defines the extent of hydrolysis, and zis the number of mer units between cross-links.

The polyacrylate absorbent containing both amide and carboxylate groupsmay be prepared either (1) by aqueous polymerization of acrylamide witha difunctional organic cross-linker such as N,N'-methylenebisacrylamidein the presence of a free radical catalyst to obtain a water-swellable,cross-linkd polyacrylamide, followed by partial hydrolysis in aqueousalkali to obtain a cross-linked polymer having both an amide and analkali metal carboxylate groups as more fully described in U.S. Pat. No.3,247,171, or (2) by copolymerization of acrylamide and acrylic acidalkali metal salt in the presence of a cross-linking monomer such asN,N'-methylenebisacrylamide and a catalyst system such as 1:1 ammoniumpersulfate and β-dimethyl-aminopropionitrile, also described in theaforesaid patent, or (3) by radiation polymerization and cross-linkingas described in U.S. Pat. No. 4,192,727.

Polyacrylate absorbents also may be prepared by subjecting linearpolyacrylate to high energy radiation cross-linking as described in U.S.Pat. No. 3,229,769, or to chemical polymerization and cross-linking asdescribed in British Pat. No. 719,330, or may be prepared bycross-linking of a previously prepared polyacrylamide.

Acrylate modified polysaccharides are those which have a polyacrylatechain grafted onto a cellulose or starch molecule. They are preferredgraft copolymers of polysaccharides which have hydrophilic chainsgrafted thereon. By "hydrophilic chain" is meant a polymer chainobtained from monomers which have a group which is water-soluble orbecomes water-soluble on hydrolysis, e.g., carboxyl, sulfonic, hydroxyl,amide, amino, quaternary ammonium and hydrolysis products thereof. Inthe polysaccharides acrylate polymers, a hydrophilic chain of thegeneral formula ##STR2## is attached to the backbone of the cellulose orstarch molecule through a carbon linkage. In the formula, ##STR3##independently represents an acid, ester, alkali metal, ammonium salt oramide group, each R independently is hydrogen or lower alkyl, r is aninteger of from 0 to about 5,000 and s is an integer of from 0 to about5,000, and r+s is at least 500.

The polysaccharide acrylate polymers may be prepared employing wellknown procedures for carrying out graft copolymerization of olefinicallyunsaturated chains onto cellulose and starch in which grafting of thehydrophilic material onto a starch or cellulose backbone is accomplishedsimultaneously with the formation of the hydrophilic polymeric material,and, if necessary, followed by hydrolysis. Thus, the polymers may beprepared by the polymerization of an appropriate polysaccharide with anappropriate acrylic monomer such as acrylonitrile, methacrylonitrile,methyl or ethyl acrylate, acrylic or methacrylic acid, or withacrylamide or methacrylamide, followed by alkaline hydrolysis or by thepolymerization of alkali metal salt of acrylic or methacrylic acid withthe appropriate polysaccharide. The polymerization is carried out in thepresence of a free radical catalyst system in an aqueous medium, or byirradiation (ultra-violet, gamma-, or X-radiation). Catalyst systems foremployment in aqueous media usually comprise an inorganic oxidizingagent as initiator and an inorganic reducing agent as activator.Representative oxidizing agent initiators are inorganic persulfates,peroxides and alkali metal bromates and chlorates. Representativereducing agent activators are alkali metal bisulfites, sulfites, ferrousammonium sulfate, and alkali metal thiosulfate.

In a method for carrying out graft polymerization employing a catalystsystem, the inorganic oxidizing agent initiator and the inorganicreducing agent activator each as an aqueous solution are alternatelyadded to a reaction medium comprising a water-solution of an acrylatemonomer, a co-monomer, a cross-linking monomer, and a dispersion ofpulverulent or fibrous water-insoluble water-swellable polysaccharide inwater-immiscible organic liquid containing a minor amount ofwater-miscible solvent to obtain an acrylate modified polysaccharideproduct as more fully described in U.S. Pat. No. 4,028,290. Othersuitable methods for chemical catalytic graft polymerization may befound in U.S. Pat. Nos. 3,256,372; 3,661,815; 4,076,663; 3,889,678 and4,105,033.

Suitable polysaccharide acrylate polymers are those in which thehydrophilic chain loading on the backbone is in the range of from about10 percent by weight to about 90 percent by weight, usually from about40 to 80 percent by weight of the polysaccharide acrylate polymer.

Other suitable water-insoluble, water-swellable polymers includecross-linked carboxymethylcellulose (CMC) obtained as described, forexample, in U.S. Pat. No. 2,639,239, cross-linked poly(alkylene oxide)of molecular weight of at least 100,000, obtained as described, forexample, in U.S. Pat. Nos. 3,956,224; 3,264,202; 3,957,605 and3,898,143; and blends of organic substances of polysaccharide character,e.g., natural or synthetic gums. It has been found generally that whengums are employed they must be employed as blends. It appears that thepolysaccharide gums which are normally soluble interact when employed asblends to have the desirable swellability without the undesirablesolubility. Typical gums which may be employed in blends include locustbean gum, guar gum, xantham gum, tragacanth gum, karaya gum and thelike. Gum blends as well as the absorbent polymers above described areavailable commercially under various trade names.

The water-insoluble, water-swellable polymers prepared by any of theforegoing methods are generally obtained as stiff, brittle solids. Thesemay be comminuted to the appropriate size. Preferably they are employedin the form of powder as previously defined, but may also be employed inother forms.

The liquid polyhydroxy compounds which are suitable from the currentlyavailable hydroxy compounds are quite limited and are substantially aspreviously defined. Commercial grades of vehicles are appropriate. It isnot necessary to subject them to drying prior to use. Although liquidssuch as propylene glycol are operable in forming the desired film, theslowness in forming the film renders them less desirable in theinvention directed to a process for immobilization.

When the solidified structure is a film or a foam sheet, it may be onlypart of a moisture receiving component of the absorbent article.However, as previously indicated, it may be obtained as a free film orfoam sheet and be employed in the ultimate absorbent article toconstitute the entire moisture receiving portion thereof. It may be usedwherever a dessicant is necessary.

The absorbent product as a free absorbent film or sheet is preferablyformed by casting on a metal surface or coating on a silicone or otherrelease agent covered surface a liquid absorbent-immobilizingcomposition comprising from about 25 to 125 parts of particulateabsorbent polymer in 100 parts of liquid polyhydroxy organic compoundand allowing the liquid composition to solidify either by heating attemperatures of from 175° F. to 450° F. for from a few seconds to about15 minutes or standing at temperature up to 175° F. for from about 30minutes to about 24 hours. The absorbent product as a coating on asubstrate is formed by coating on the ultimate substrate under similarconditions.

The absorbent product as a solidified structure may be in the form offilament or rope. Such form may be achieved readily by meteringabsorbent and polyhydroxy compound into a cold extruder with the dieheated to a temperature in the range of 175° F. to 450° F. andrecovering the extruded filament or rope.

The preferred absorbent product as an immobilized structure is in theform of foam. The foam product in the shape of a sheet is preferablyobtained by casting or coating on metal surface or on a silicone orother release agent coated surface a liquid absorbent-immobilizingcomposition comprising from about 25 to 125 parts of particulateabsorbent polymer and 2 to 30 parts by weight of blowing agent for 100parts by weight of liquid polyhydroxy organic compound, and allowing thecoated liquid composition to stand at temperatures up to about 175° F.for from about 30 minutes to 24 hours, or by heating the coatedcomposition from 175° F. to 450° F. for from a few seconds to aboutfifteen minutes.

When the absorbent product is a foam product to be employed as aprotective liner of a dual-walled container, the liquid immobilizingabsorbent composition is poured into the area between the containerwalls and allowed to stand at ambient temperature or heated as for thefoam sheets.

The actual amounts of absorbent in the compositions within the scopepreviously indicated is dependent on the level of absorption required inthe ultimate environment. Thus, if the absorption is to be accomplishedby a diaper, and the substrate is a diaper pad, the liquid absorbentimmobilizing composition with or without blowing agent will containabsorbent sufficient to supply the desired absorptive capacity to thepad substrate. The products and processes are useful in the manufactureof numerous absorbent articles. They are especially useful wherereduction in bulk of absorbent as well as high capacity is desirable,such as in articles to be worn. Thus, they are particularly useful fordiapers and incontinence pads, but also for sanitary napkins, bandagesand the like. Both the film and foam form of the product are usefulalthough the latter is preferred. In use in diapers, the absorbentproduct may be as a sole absorbent or as a component improving thequality of the existing absorbent. In the manufacture of diapers inwhich the film or foam product is incorporated as an improvement to theliquid receiving portion of the diaper, the composition is applied tothe surface of the aqueous liquid receiving portion of the article,namely the batting, the coated batting subjected to a heating cycle orto standing at temperatures up to 175° F., and the resulting modifiedbatting provided with moisture impermeable backing and a moisturepermeable top sheet. Alternatively, the absorbent immobilizingcomposition may be coated on a conventional non-absorbent moistureimpermeable diaper backing without batting and thereafter laminated witha conventional moisture permeable top sheet to provide a thin diaper.The foam product is particularly adaptable to this use. Other techniqueswithin the skill of those to whom the invention is directed may beemployed to obtain new absorbent diapers.

In the case of sanitary napkins, the absorbent immobilizing compositionmay be applied to the cellulosic absorbent surface and wrapped in aconventional manner to produce a napkin of improved absorptive capacity.

In the case of bandages, the absorbent composition may be coated onto anaqueous liquid permeable but a gel impervious materials, e.g., non-wovenfabrics such as of rayon or polyester fabrics, and then inserted in thegauze bandage.

The following examples illustrate the invention but are not to beconstrued as limiting:

EXAMPLES I-VIII

Absorbent compositions set forth in Table A are prepared.

                                      TABLE A                                     __________________________________________________________________________                            Amount of Components                                                          (parts by weight)                                                             Examples                                              Component               I  II III                                                                              IV V  VI VII                                                                              VIII                             __________________________________________________________________________    Absorbent                                                                     Starch Polyacrylate,.sup.+                                                                            50                                                    (SGP 502S, Henkel)                                                            Starch Polyacrylate.sup.+  25                                                 (Stasorb ®, A. E. Staley)                                                 Gum Blend.sup.++ (GFS, Kelko, Div. Merck & Co.)                                                             70                                              Cross-linked Poly(Sodium, acrylate),                                                                           70                                           (Favorsab ®, Stockhausen)                                                 Cross-linked Ionic Polyacrylate     70                                        Permasorb ® AG, National Starch)                                          Cross-linked Ionic Polyacrylate        30                                     (Permasorb ® ZO, National Starch)                                         Starch Polyacrylate (35A 100, Grain Products)                                                                           70                                  Cross-linked Carboxymethylcellulose,         80                               (Akucell ® SW, Enka Industries)                                           Liquid Polyhydroxy Compound                                                   Glycerol                   100         100                                    Ethylene Glycol         100   100                                                                              100                                                                              100   100                                                                              100                              __________________________________________________________________________     .sup.+ Hydrolyzed polyacrylonitrile grafted to starch                         .sup.++ Blend of xanthan gum, locust bean gum and guar gum               

The products having the compositions identified in Table A are employedto coat substrates to produce absorbent articles as follows:

The products having the compositions of Examples I, IV, and VI areemployed to coat diaper topsheet materials (a) a nonwoven fabric sheetcomprising 1.5 to 3.0 denier rayon and containing 20 to 35 percentacrylate ester copolymer binder, and having a weight of about 15 to 19grams per square yard, and (b) a nonwoven fabric sheet comprising 35 to64 percent 1.5 to 3.0 denier polyester fiber, 14 to 40 percent 1.5 to3.0 denier rayon fibers and 20 to 30 percent of the same acrylate estercopolymer binder, and having a weight of about 25 to 35 grams per squareyard. The modified topsheet materials when employed to produce diapersor when employed as an insert in disposable diapers produce diapershaving superior absorption properties and in which the particulateabsorbents are found to be substantially completely immobile.

The products having the compositions of Examples III and VII areemployed to saturate creped paper. The modified papers are employed toproduce inserts for absorbent bed paddings.

The products having the compositions of Examples V and VIII are employedto coat polyethylene film to be employed as backing for disposablediapers. The modified backing is then overlaid with fluffed cellulosefibers forming a laminate then with overlaid with nonwoven fabric web toproduce a superior absorbent diaper.

The product having the composition of Examples II is employed to coatnonwoven fabric of rayon, above described, and thereafter laminated withthe same material to use as inserts for napkins and bandages.

In use, each of the products exhibits superior absorption propertiesattributable to the particulate absorbent borne thereon. Further it isfound that the particulate absorbent materials are not dislodged onstorage, shipping or use.

EXAMPLES X--XVII

Foamable compositions as set forth in Table B are first prepared byfirst mixing together at ambient temperature the appropriate absorbentand blowing agent, thereafter adding the appropriate liquid polyhydroxyorganic compound, and mixing to a smooth dispersion.

                                      TABLE B                                     __________________________________________________________________________                      Amount of Components                                                          (parts by weight)                                                             Examples                                                    Component         X  XI XII                                                                              XIII                                                                             XIV                                                                              XV XVI                                                                              XVII                                   __________________________________________________________________________    Absorbent                                                                     Starch Polyacrylate                 50                                        (SPC 502S, Henkel)                                                            Starch Polyacrylate              50                                           (Stasorb ®, A. E. Staley)                                                 Cross-linked Ionic Polyacrylate                                                                 50 75 50                                                    (Permasorb ® AG, National Starch)                                         Polyacrylate                  50                                              (Sanwet ®, Sanyo)                                                         Polyacrylate               50                                                 (Aqua-Keep, Mitsubishi)                                                       Cellulose Polyacrylate*                50                                     Polyhydroxy Compound                                                          Glycerol          100   100                                                                              100                                                                              100                                             Ethylene Glycol      100         100                                                                              100                                                                              100                                    Blowing Agent                                                                 Celogen ® OT.sup.1   5                                                    Celogen ® TSH.sup.2     5           5                                     Celogen ® AZ.sup.3         5     5                                        Sodium Bicarbonate                                                                               5 10           5                                           __________________________________________________________________________     *Prepared according to U.S. Pat. No. 3,889,678                                .sup.1 p,pOxybisbenzene sulfonyl hydrazide;                                   .sup.2 pToluene sulfonyl hydrazide;                                           .sup.3 Azodicarbonamide; all products of Uniroyal Chemical               

In separate operations, portions of each composition are treated in thefollowing manner: (a) knife-coated onto a release-coated paper, (b)knife-coated onto a polyethylene film, and (c) poured into the spacebetween the inner glass and outer metal walls of a dual-wall containeruntil about one-tenth of the space is filled. The treated compositionsare allowed to stand at ambient temperature whereupon foaming occurs ina few hours and there are obtained (a) foam sheets from the compositionswhich have been knife-coated onto release coated paper; (b) foam-coatedfilm from compositions which have been knife-coated onto polyethylenefilm; and (c) foam in the space near the bottom portion of the doublewall container.

The operation is repeated except that the treated samples are exposed toa temperature of about 275° F. for ten seconds to obtain thecorresponding foam products.

When about 100 grams of water is applied to foam (about 10 gram size) ineach of the foregoing examples, the foam swells instantaneously takingup the water substantially completely.

EXAMPLE XVIII

A foamable composition is prepared by mixing together at ambienttemperature 80 parts of starch polyacrylate (Stasorb®) and 5 parts ofsodium bicarbonate, and then adding and mixing 100 parts of glycerol. Inseparate operations, the composition is knife-coated onto (a) nonwovencellulosic fabric, (b) polyethylene film, and (c) thin layer of woodpulp material as substrates. The coated substrates are exposed to atemperature of 300° F. for a few seconds to obtain foam coatedsubstrates. The foam coated substrates are then slit into sizes suitablefor absorbent articles.

When water is applied to the articles comprising foam coated substrates,there is instantaneous removal of freestanding water and swelling of thefoam.

I claim:
 1. A process for producing an absorbent bearing foam productcomprising:(1) feeding into a cold extruder the components of a liquidfoam-forming composition comprising a particulate water-insoluble,water-swellable absorbent polymer having a gel capacity of at least 10,a liquid polyhydroxy organic compound, and a blowing agent, wherein theamounts of the components are from about 25 to about 125 parts by weightof the absorbent polymer and from about 2 to about 30 parts by weight ofblowing agent for every 100 parts by weight of liquid polyhydroxyorganic compound; (2) passing the components through an extruder barrelat ambient temperature to intimately mix the components; (3) forcing theresulting mixture into a die maintained at temperatures in the range ofabout 200° to 400° F. to cause foam formation; (4) expelling the foamthrough the orifice of the heated die onto a temporary or permanentsubstrate; and (5) allowing the foam to solidify into an absorbentbearing solidified structure.
 2. A process according to claim 1 in whichthe particular absorbent is an acrylate polymer or acrylate modifiedpolysaccharide and the polyhydroxy organic compound is glycerol orethylene glycol.
 3. A process according to claim 1 in which the foam isexpelled onto a permanent substrate to obtain the product as a foamcoated absorbent article.
 4. A process according to claim 1 in which thefoam is expelled onto a temporary substrate suitable for stripping,thereafter stripping to obtain the product as a self-supporting foamsheet or strip.